/Engine/Source/Runtime/Experimental/Chaos/Public/Framework/Threading.h
A non-yielding, recursive spin lock Implements a first-in, first-out lock / mutex that won't yield back to the system. Intended for applications that must wake / resume at the earliest opportunity. Each thread attempting a write gets an atomically controlled counter to wait on so the lock is fair in that the locks will be ordered according to the order Lock was called.
class FPhysSpinLock